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Water heaters for use with Natural and L.P.G.

GWH 425 HN

Flow Modulated with Electronic Ignition

Suitable for heating potable water only - Not approved for space heating purposes

(Intended for variable flow applications with steady cold water inlet temperatures)

GWH-425-HN-N
GWH-425-HN-L

720 

607

 026 

US

 (

04.

11) 

A

L

Warning: 

If  the  information  in  this  manual  is  not

followed  exac tly,  a  fire  or  explosion  may  result
causing property damage, personal injury or death.
Do  not  store  or  use  gasoline  or  other  flammable
vapor and liquids in the vicinity of this or any other
appliance.

Improper 

installation, 

adjustment, 

alteration,

service  or  maintenance  can  cause  injury  or
property  damage.  Refer  to  this  manual.  For
assistance  or  additional  information  consult  a
qualified  installer,  service  agency  or  the  gas
supplier.
In  the  Commonwealth  of  Massachusetts  this
product must be installed by a licensed plumber or
gas fitter.

Upon  completion  of  the  installation,  these
instructions  should  be  handed  to  the  user  of  the
appliance for future reference.

What to do if you smell gas

• Close gas valve. Open windows.

• Do not try to light any appliance

• Do  not  touch  any  electrical  switch;  do  not  use  any

phone in your building

• If  you  cannot  reach  your  gas  supplier,  call  the  fire

department.

• Immediately call your gas supplier from a neighbor’s

phone. Follow the gas supplier’s instructions.

• Installation  and  service  must  be  performed  by  a

qualified installer, service agency or the gas supplier.

Summary of Contents for GWH 425 HN

Page 1: ...aintenance can cause injury or property damage Refer to this manual For assistance or additional information consult a qualified installer service agency or the gas supplier In the Commonwealth of Massachusetts this product must be installed by a licensed plumber or gas fitter Upon completion of the installation these instructions should be handed to the user of the appliance for future reference ...

Page 2: ...er appliance WHAT TO DO IF YOU SMELL GAS Do not try to light any appliance Do not touch any electrical switch do not use any phone in your building Immediately call your gas supplier from a neighbor s phone Follow the gas supplier s instructions If you cannot reach your gas supplier call the fire department Installation and service must be performed by a qualified installer service agency or the g...

Page 3: ... will not exceed the heating capacity of the heater On Off Switch to activate system Red LED indicator flashes with low water pressure Green LED indicator main burner operation BOSCH is constantly improving our products therefore specifications are subject to change without prior notice 425 HN LP and 425 HN NG Specifications Gas Input max 117 000 Btu hr min 28 000 Btu hr Water Connection Thread fi...

Page 4: ...INIMUM INSTALLATION CLEARANCES FROM COMBUSTIBLE AND NON COMBUSTIBLE MATERIALS FOR ALCOVE OR CLOSET INSTALLATIONS FRONT VIEW SIDE VIEW MODEL 425HN MODEL 425 HN TOP A 12 FRONT B 4 BACK 0 SIDES 4 FLOOR C 12 VENT DIAMETER 5 ...

Page 5: ...control which has been underwater PROPER LOCATION FOR INSTALLING YOUR HEATER Carefully select the location of your new heater For your safety and for proper heater operation you must provide an abundant supply of combustion air and a proper venting Fig 1 Water heater drain plug The heater may still operate even when improperly vented It will however be less efficient and could eventually damage th...

Page 6: ...00 Btu hr if all air is taken from the outside by horizontal ducts 4000 Btu hr if all air is taken from the outside by direct openings or vertical ducts Or the confined space must be provided with one permanent opening or duct that is within 12 inches of the ceiling of the enclosure This opening must have a minimum free area of one square inch per 3000 Btu hr if all air is taken from the outside b...

Page 7: ...s stamped with a number 79 for LPG and 120 for Natural Gas Fig 2 Mounting the Heater WALL STUDS 1 X 4 SPACE BOARD SUPPORT BOARD 13 Fig 3 Incandescent Particle Tray Illustration The incandescent particle tray shipped loose in the carton with the water heater must be attached at the bottom of the water heater front cover at the time of installation Use the screws provided See figure 3 SCREWS INCANDE...

Page 8: ...ter heater to a masonry chimney the following connector guidelines must be followed for safe and proper operation An approved gas vent connector must be attached to the top of the water heater and rise vertically at least 12 before entering into an approved gas vent connector elbow Any gas vent section that is greater than 45 degrees from the vertical is considered horizontal If a horizontal vent ...

Page 9: ...the gas lines or malfunction of the supply system the gas valve and regulator must be checked for safe operation Make sure that the regulator vent is protected against blockage When your connections are made check for gas leaks at all joints not just the ones you made Apply some soapy water to all gas fittings and gas valve Soap bubbles are a sign of a leak NOTE Do not apply soap solution to the p...

Page 10: ...l length of piping and then adding 5 ft for every elbow or T to the actual length Use the charts below to determine the pipe diameter necessary to accommodate the BTU demand of the unit If there are more gas drawing appliances on the line size according to the maximum amount of BTU demand Follow boxed numbers for piping just one 425 HN example 3 4 B I Natural Gas pipe for 30 ft will handle 152 000...

Page 11: ...runs as short as possible When facing the heater the cold water inlet will be on the right and the hot water outlet on the left Although water piping throughout the building may be other than copper copper or galvanized piping should be used when connecting to the heaters male NPT flex connectors follow local codes if more stringent Plastics or other PEX type plumbing line materials are not suitab...

Page 12: ...icator light is flashing this is a warning that the water pressure is not enough to ignite the main burner 6 Turn the hot water faucet on to the minimum flow rate required to activate the heater The automatic ignition system first ignites the safety pilot burner which then ignites the main burner in about 4 seconds 7 The green LED indicator is on when the main burner is on 8 The pilot flame will e...

Page 13: ...ers have yellow flames while others have good flames it is likely that dust lint or spider webs have partially clogged the burner venturis To clean the burners contact a gas service person Mineral Scale Build up The 425 HN heater when operated at lower temperature settings does not accumulate mineral build up If however the heater is used at the higher temperature settings and the water has a high...

Page 14: ...and component parts must be totally free of dirt In hard water areas mineral deposits can eventually 3 5 years in hard water areas corrode the water valve parts to a point where they will need replacing Any sign of moisture or corrosion at the joint of the water valve and the gas valve is a sign that the water valve components need to be serviced immediately 7 Poor circuit connections at the ECO o...

Page 15: ...is mixing with the hot water between the 425 HN and the outlet Compare water temperature at outlet of the 425 HN hold the 425 HN outlet pipe with your hand and at the tap If these two are very different check for mixing valve or plumbing crossover see NO SPARK AT THE PILOT paragraph 4 5 Parts in water valve are dirty or damaged which will prevent the gas valve from being fully opened Water valve m...

Page 16: ... reduce such hot water temperature in the event of any temperature instability with the use of a temperature balance shower valve refer to shower valve manufactures instructions for internal adjustment setting Adjustments should be made to the hottest setting in the shower valve Additionally the temperature control of the heater can be adjusted to produce a more comfortable hot water temperature S...

Page 17: ...ner manifold gas pressure test nipple 4 Main gas burner 5 Pilot gas tubing 6 LED failure indicator 7 on off switch 8 LED operation indicator 9 Water valve 10 Temperature adjustment selector 11 Gas inlet gas pressure test nipple 12 Hose 3 1 4 10 11 2 9 8 6 7 5 12 6 720 606 804 10 1AL ...

Page 18: ...18 6 720 607 026 Fig 15 INTERIOR COMPONENTS DIAGRAM AND PARTS LIST ...

Page 19: ...7 Pilot electrovalve 8 708 501 249 18 Burner electrovalve 8 708 501 250 19 O ring 8 700 205 023 20 Hydro generator 8 707 406 043 21 Cold water pipe 8 700 705 947 22 Outlet flex hose 8 700 703 139 23 Washer 8 700 103 658 24 Water valve 8 707 002 649 25 Water valve cover 8 705 500 101 26 Diaphragm 8 700 503 053 27 Water inlet filter 8 700 507 001 28 Water valve selector screw 8 708 500 289 29 Volume...

Page 20: ...20 6 720 607 026 Fig 16 Flow chart of 425 HN ...

Page 21: ... may not apply to you This warranty gives specific legal rights You may also have other rights which vary from state to state Fifteen Year Limited Warranty General BOSCH PRO water heaters are warranted by the Manufacturer BOSCH through Controlled Energy Corp Controlled Energy Corp CEC will furnish a replacement heat exchanger and will furnish a replacement of any other part which fails in normal u...

Page 22: ...22 6 720 607 026 ...

Page 23: ...23 6 720 607 026 ...

Page 24: ...k Waitsfield Vermont 05673 Phone 866 330 2730 Fax 802 496 6924 www protankless com techsupport protankless com 3 1 e g a p e e s E L B A T E C N A N E T N I A M R A E Y Y R E V E S R A E Y 2 Y R E V E S R A E Y 5 3 Y R E V E E V L A V R E T A W E T A C I R B U L E V L A V R E T A W D L I U B E R N E E R C S R E T L I F R E T A W T C E P S N I Y L B M E S S A T O L I P T C E P S N I Y L B M E S S A...

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